States are divided into counties or county-equivalents, which may be assigned some local governmental authority but are not sovereign. County or county-equivalent structure varies widely by state. Kentucky, Massachusetts, Pennsylvania, and Virginia use the official title of Commonwealth rather than State.

Over time, the U.S. Constitution has been amended, and the interpretation and application of its provisions have changed. The general tendency has been toward centralization and incorporation, with the federal government playing a much larger role than it once did. There is a continuing debate over states' rights, which concerns the extent and nature of the states' powers and sovereignty in relation to the federal government as well as the rights of individual persons. Debates over states' rights were a contributing factor to the outbreak of the American Civil War.

The United States Congress may admit new states on an equal footing with existing ones; this last happened in 1959 with the admission of Alaska (Jan. 3) and Hawaii (Aug. 21). The U.S. Constitution is silent on the question of whether states have the power to leave, or secede from, the Union, but the U.S. Supreme Courthas ruled[4][5] unilateral secession to be unconstitutional, a position driven in part by the outcome of the American Civil War.

Since the early 20th century, the Supreme Court of the United States has interpreted the Commerce Clause of the Constitution of the United States to allow greatly expanded scope of federal power over time, at the expense of powers formerly considered purely states matters. The Cambridge Economic History of the United States says, "On the whole, especially after the mid-1880s, the Court construed the Commerce Clause in favor of increased federal power."[6] In Wickard v. Filburn 317 U.S.111 (1942), the court expanded federal power to regulate the economy by holding that federal authority under the commerce clause extends to activities which are local in character.[7]

For example, Congress can regulate railway traffic across state lines, but it may also regulate rail traffic solely within a state, based on the theory that wholly intrastate traffic can still have an impact on interstate commerce. In recent years, the Court has tried to place limits on the Commerce Clause in such cases as United States v. Lopez and United States v. Morrison.[clarification needed]

Another source of congressional power is its spending power—the ability of Congress to impose taxes and distribute the resulting revenue back to the states (subject to conditions set by Congress). A classic example of this is the system of federal-aid highways, which includes the Interstate Highway System. The system is mandated and largely funded by the federal government, and also serves the interests of the states. By threatening to withhold federal highway funds, Congress has been able to pressure state legislatures to pass a variety of laws. An example of this is the nationwide legal drinking age of 21, enacted by each state, brought about by the National Minimum Drinking Age Act. Although some objected that this infringes on states' rights, the Supreme Court upheld the practice as a permissible use of the Constitution's Spending Clause in South Dakota v. Dole 483 U.S.203 (1987).

In practice, each state has adopted a three-branch system of government (with legislative, executive, and judiciary branches) generally along the same lines as that of the federal government—though this is not a requirement.

In all of the U.S. states, the chief executive is called the Governor, who serves as both the ceremonial head of state and administrative head of government. The governor may approve or veto bills passed by the state legislature, as well as push for the passage of bills supported by the party of the Governor. In 43 states, governors have line item veto power.[8]

Most states have a "plural executive" in which two or more members of the executive branch are elected directly by the people. Such additional elected officials serve as members of the executive branch, but are not beholden to the governor and the governor cannot dismiss them. For example, the attorney general is elected, rather than appointed, in 43 of the 50 U.S. states.

The legislatures of 49 of the 50 states are made up of two chambers: a lower house (termed the House of Representatives, State Assembly, General Assembly or House of Delegates) and a smaller upper house, always termed the Senate. The exception is the unicameralNebraska Legislature, which is composed of only a single chamber.

Most states have part-time legislatures, while six of the most populated states have full-time legislatures. However, several states with high population have short legislative sessions, including Texas and Florida.[9]

In Baker v. Carr (1962) and Reynolds v. Sims (1964), the U.S. Supreme Court held that all states are required to elect their legislatures in such a way as to afford each citizen the same degree of representation (the one person, one vote standard). In practice, most states choose to elect legislators from single-member districts, each of which has approximately the same population. Some states, such as Maryland and Vermont, divide the state into single- and multi-member districts, in which case multi-member districts must have proportionately larger populations, e.g., a district electing two representatives must have approximately twice the population of a district electing just one.

If the governor vetoes legislation, all legislatures may override it, usually, but not always, requiring a two-thirds majority.

In 2013, there were a total of 7,383 legislators in the 50 state legislative bodies. They earned from $0 annually (New Mexico) to $90,526 (California). There were various per diem and mileage compensation.[10]

States can also organize their judicial systems differently from the federal judiciary, as long as they protect the federal constitutional right of their citizens to procedural due process. Most have a trial level court, generally called a District Court or Superior Court, a first-level appellate court, generally called a Court of Appeal (or Appeals), and a Supreme Court. However, Oklahoma and Texas have separate highest courts for criminal appeals. New York State has its own terminology, in that the trial court is called the Supreme Court. Appeals are then taken to the Supreme Court, Appellate Division, and from there to the Court of Appeals.

Most states base their legal system on English common law (with substantial indigenous changes and incorporation of certain civil law innovations), with the notable exception of Louisiana, a former French colony, which draws large parts of its legal system from French civil law.

Only a few states choose to have the judges on the state's courts serve for life terms. In most of the states the judges, including the justices of the highest court in the state, are either elected or appointed for terms of a limited number of years, such as five years, eligible for re-election or reappointment if their performance is judged to be satisfactory.

Under Article Four of the United States Constitution, which outlines the relationship between the states, the United States Congress has the power to admit new states to the Union. The states are required to give full faith and credit to the acts of each other's legislatures and courts, which is generally held to include the recognition of legal contracts and criminal judgments, and before 1865, slavery status. Regardless of the Full Faith and Credit Clause, some legal arrangements, such as professional licensure and marriages (e.g. same-sex marriages), may be state-specific, and until recently states have not been found by the courts to be required to honor such arrangements from other states.[11]

Such legal acts are nevertheless often recognized state-to-state according to the common practice of comity. States are prohibited from discriminating against citizens of other states with respect to their basic rights, under the Privileges and Immunities Clause. Under the Extradition Clause, a state must extradite people located there who have fled charges of "treason, felony, or other crimes" in another state if the other state so demands. The principle of hot pursuit of a presumed felon and arrest by the law officers of one state in another state are often permitted by a state.[12]

With the consent of Congress, states may enter into interstate compacts, agreements between two or more states. Compacts are frequently used to manage a shared resource, such as transportation infrastructure or water rights.[13]

The order in which the original 13 states ratified the constitution, then the order in which the others were admitted to the union. (Click to see animation)

Since the establishment of the United States in 1776, the number of states has expanded from the original 13 to 50. The U.S. Constitution provides that "New States may be admitted by the Congress into this Union" and forbidding a new state to be created out of the territory of an existing state, or the merging of two or more states into one, without the consent of both Congress and all the state legislatures involved."

In practice, most of the states admitted to the union after the original 13 have been formed from Territories of the United States (that is, land under the sovereignty of the federal government but not part of any state) that were organized (given a measure of self-rule by the Congress subject to the Congress' plenary powers under the territorial clause of Article IV, sec. 3, of the U.S. Constitution).[15]

Generally speaking, the organized government of a territory made known the sentiment of its population in favor of statehood, usually by referendums. Congress then directed that government to organize a constitutional convention to write a state constitution. Upon acceptance of that Constitution, Congress has always admitted that territory as a state. The broad outlines in this process were established by the Northwest Ordinance (1787), which predated the ratification of the Constitution.

However, Congress has ultimate authority over the admission of new states, and is not bound to follow this procedure. A few U.S. states (outside of the original 13) that were never organized territories of the federal government have been admitted:

Congress is also under no obligation to admit states even in those areas whose population expresses a desire for statehood. For instance, the Republic of Texas requested annexation to the United States in 1837, but fears about potential conflict with Mexico delayed the admission of Texas for nine years.[17]

Once established, most state borders have been generally stable, with exceptions including the formation of the Northwest Territory in 1787 and the Southwest Territory in 1790 from various portions of the original states, the cession by Maryland and Virginia of land to create the District of Columbia in 1791 (Virginia's portion was returned in 1847), and the creation of states from other states, including the creation of Kentucky and West Virginia from Virginia, and Maine from Massachusetts. However, there have been numerous minor adjustments to state boundaries over the years due to improved surveys, resolution of ambiguous or disputed boundary definitions, or minor mutually agreed boundary adjustments for administrative convenience or other purposes.[16] One notable example is the case New Jersey v. New York, in which New Jersey won roughly 90% of Ellis Island from New York in 1998.[18]

Puerto Rico referred to itself as the "Commonwealth of Puerto Rico" in the English version of its constitution, and as "Estado Libre Asociado" (literally, Associated Free State) in the Spanish version.

A non-binding referendum on statehood, independence, or a new option for an associated territory (different from the current status) was held on November 6, 2012. Sixty one percent (61%) of voters chose the statehood option, while one third of the ballots were submitted blank.[20][21]

Some residents of the District support statehood of some form for that jurisdiction—either statehood for the whole district or for the inhabited part, with the remainder remaining under federal jurisdiction.

The State of Franklin existed for four years not long after the end of the American Revolution, but was never recognized by the union, which ultimately recognized North Carolina's claim of sovereignty over the area. A majority of the states were willing to recognize Franklin, but the number of states in favor fell short of the two-thirds majority required to admit a territory to statehood under the Articles of Confederation. The territory comprising Franklin later became part of the state of Tennessee.

The State of Superior was a proposed state formed out of the Upper Peninsula of Michigan. Several prominent legislators including local politician Dominic Jacobetti formally attempted this legislation in the 1970s, with no success. As a state, it would have had, by far, the smallest population, and remaining so through the present day. Its 320,000 residents would equal only 60% of Wyoming's population, and less than 50% of Alaska's population.

The State of Sequoyah began in the early 1900s during a meeting of the Cherokee, Choctaw, Creek, Chickasaw and Seminole Native American nations. At the time, the eastern part of what would later become Oklahoma encompassed the Indian Territory. The proposed constitution ultimately failed in the U.S. Congress, which balked at adding two new western states. Instead, the Indian Territory was incorporated into the new state of Oklahoma in 1907, yet many of Sequoyah's principles lived on.

The State of Absaroka, aka "state that never was," grew out of the political discontent of the Great Depression. Frustrated with the U.S. government, a group of politicians and businessmen, led by former minor league baseball player A.R. Swickard, planned to create a new state called Absaroka. Their statehood movement began in 1939. The proposed state included large swaths of Wyoming, Montana and South Dakota, and encompassed famous landmarks such as the Grand Tetons and Yellowstone National Park. Despite its initial popularity, the statehood movement's novelty quickly wore off, and an official proposal for secession was never drafted. The movement was unsuccessful and fairly short-lived.[23]

Lincoln is another state that has been proposed multiple times. It generally consists of the eastern portion of Washington state and the panhandle of the northern portion of Idaho. It was originally proposed by Idaho in 1864 to include just the panhandle of Idaho, and again in 1901 to include eastern Washington. Proposals have come up in 1996, 1999, and 2005.

The Constitution is silent on the issue of the secession of a state from the union. However, its predecessor document, the Articles of Confederation, stated that the United States "shall be perpetual." The question of whether or not individual states held the right to unilateral secession remained a difficult and divisive one until the American Civil War. In 1860 and 1861, eleven southern states seceded, but following their defeat in the American Civil War were brought back into the Union during the Reconstruction Era. The federal government never recognized the secession of any of the rebellious states.[4][5]

Following the Civil War, the United States Supreme Court, in Texas v. White, held that states did not have the right to secede and that any act of secession was legally void. Drawing on the Preamble to the Constitution, which states that the Constitution was intended to "form a more perfect union" and speaks of the people of the United States in effect as a single body politic, as well as the language of the Articles of Confederation, the Supreme Court maintained that states did not have a right to secede. However, the court's reference in the same decision to the possibility of such changes occurring "through revolution, or through consent of the States," essentially means that this decision holds that no state has a right to unilaterally decide to leave the Union.[4][5]

Four of the states bear the formal title of commonwealth: Kentucky, Massachusetts, Pennsylvania, and Virginia. This is merely a legacy of all four states' history, and their formal name has no effect on their legal status as states.

Of the remaining names, 22 are from European languages: Seven from Latin (mainly Latinized forms of English names), the rest are from English, Spanish and French. Eleven states are named after people, including seven named for royalty and one named after an American president. The origins of six state names are unknown or disputed.

States may be grouped in regions; there are endless variations and possible groupings, as most states are not defined by obvious geographic or cultural borders. For further discussion of regions of the U.S., see the list of regions of the United States.

The northern and southern borders of the Thirteen Colonies on the East Coast were largely determined by colonial charters and anchoring coastal settlements. The western boundaries were determined by the limits of transportation, the infeasibility of settling areas dominated by Native Americans and foreign powers, and the decision to create new states out of western territories.

Most borders beyond the Thirteen Colonies were created by Congress as it created territories, divided them, and turned them into states as they became more populated. Territorial and new state lines followed various geographic features, economic units, and the pattern of settlement. In the West, relatively arbitrary straight lines following latitude and longitude often prevail, due to the sparseness of settlement west of the Mississippi River.

^a. Third Constitution of Kentucky (1850), Article 2, Section 1 ff. Other portions of the same Constitution refer to the "State of Kentucky"
b. Constitution of the Commonwealth of Massachusetts, Preamble.
c. Constitution of Pennsylvania, Preamble.
d. Constitution of Virginia (1971), Article IV, Section 1.

^U.S. Const. art. IV, § 3, cl. 2 ("The Congress shall have Power to dispose of and make all needful Rules and Regulations respecting the Territory or other Property belonging to the United States...").